Gaming machines such as slot machines, poker machines, fruit machines, and the like generally attract enormous popularity from players in casinos. Such a gaming machine displays an arrangement of symbols on the front thereof, and randomly changes types of symbols in the arrangement at each round of game. A player places a bet at the start of each round. If a winning combination appears in the arrangement, the player will win an amount of a payout that depends on the amount of the bet and the type of the winning combination.
This type of gaming machine is generally equipped with mechanical reels that are coaxially arranged and allowed to independently spin by respective motors. Symbols are permanently displayed, e.g., printed on the circumferential surfaces on each reel in a predetermined order. Mechanical reels repeat spins and stops, and thereby change visible symbols at random. Alternatively, this type of gaming machine may use an electric display device to display symbols in graphic form on a screen thereof. The symbols are aligned in two or more columns, i.e., video reels. Like mechanical reels repeating spins and stops, video reels repeatedly change in appearance, and thereby symbols repeatedly move and stop in a vertical direction. Such actions of symbols are often referred to as “spins and stops of video reels”. There is also a mechanical reel with one or more electric display devices mounted on the circumferential surface of the mechanical reel. Symbols are displayed in graphic form on a screen of the electric display device. Visible symbols move and change, whichever the mechanical reel spins or the electric display device changes images produced thereon.
Most players prefer a gaming machine that can provide a larger amount of payout. The upper limit of payout per round generally depends on a total number of types of symbol arrangements visible on reels. Mechanical reels have a limited number of symbol types mainly because of their sizes. In order to increase the upper limit of payout per round, a gaming machine with mechanical reels randomly provides a player with a right to play a bonus round. A player can win a larger amount of payout, or an amount of payout more frequently at a bonus round than at a normal round. In addition, a player can play a bonus round for free.
On the other hand, video reels have no limited number of symbol types in principle. However, a gaming machine with video reels also provides a player with a right to play a bonus round in order to enhance the variety of game contents and visual effects, and thereby attract a larger number of players.
Recent remarkable progress on game controllers, computer graphics, and display devices enables gaming machines to produce more various types of bonus rounds with more complex rules and visual effects. This facilitates differentiation of a type of gaming machines from others. On the other hand, excessively complex rules and visual effects may prevent gaming machines to raise players' expectations for winning In addition, excessively complex rules and visual effects may place a heavy burden on game designers and developers.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved gaming machine that can produce a bonus round with more simple rules and visual effects, and thereby cause a player to recognize the bonus round more clearly and reduce a burden on game designers and developers. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.